Explicit Limits Research Articles

Advancing parabolic operators in thermodynamic MHD models II: Evaluating a Practical Time Step Limit for Unconditionally Stable Methods

Unconditionally stable time stepping schemes are useful and often practically necessary for advancing parabolic operators in multi-scale systems. However, serious accuracy problems may emerge when taking time steps that far exceed the explicit stability limits. In our previous work, we compared the accuracy and performance of advancing parabolic operators in a thermodynamic MHD model using an implicit method and an explicit super time-stepping (STS) method. We found that while the STS method outperformed the implicit one with overall good results, it was not able to damp oscillatory behavior in the solution efficiently, hindering its practical use. In this follow-up work, we evaluate an easy-to-implement method for selecting a practical time step limit (PTL) for unconditionally stable schemes. This time step is used to ‘cycle’ the operator-split thermal conduction and viscosity parabolic operators. We test the new time step with both an implicit and STS scheme for accuracy, performance, and scaling. We find that, for our test cases here, the PTL dramatically improves the STS solution, matching or improving the solution of the original implicit scheme, while retaining most of its performance and scaling advantages. The PTL shows promise to allow more accurate use of unconditionally stable schemes for parabolic operators and reliable use of STS methods.

Whatever-it-takes policymaking during the pandemic

Central banks across the globe introduced large-scale asset purchase programs to address the unprecedented circumstances experienced during the pandemic. Many of these programs were announced as open-ended to shock-and-awe market participants and restore confidence in financial markets. This paper examines whether these whatever-it-takes announcements had larger effects than announcements with explicit limits on scale. We use a narrative approach to categorize announcements made by twenty-two central banks, and event study, propensity-score-matching, and local projection methods to measure the short-term effects of policy announcements on exchange rates and sovereign bond yields. We find that on average a central bank’s first whatever-it-takes announcement lowers 10-year bond yields by an additional 47 basis points relative to size-limited announcements, suggesting that communication of potential policy scale matters. Our results for yields hold for both advanced and emerging economies, while exchange rates go in opposing directions, muting their response when we group all countries together.

Principal component analysis of infinite variance functional data

Principal Components Analysis is a widely used approach of multivariate analysis. Over the past 30 years, it has gained renewed attention in the context of functional data, chiefly as a commonly used tool for dimension reduction or feature extraction. Consequently, a large body of statistical theory has been developed to justify its application in various contexts. This theory focuses on the convergence of sample PCs to their population counterparts in a multitude of statistical models and under diverse data collection assumptions. What such results have in common is the assumption that the population covariance operator exists.This paper is concerned with multivariate and functional data that have infinite variance and, consequently, for which the population covariance operator is not defined. However, the sample covariance operator and its eigenfunctions are always defined. It has been unknown what the asymptotic behavior of these important statistics is in the context of infinite variance multivariate or functional data. We derive suitable large sample theory. In particular, we specify normalizing sequences and conditions for suitably defined consistency. We study multivariate models in which explicit limits can be derived. These examples show that definitions, results and intuition developed for multivariate and functional data with finite variance need not apply in the setting we consider.

Quantifying Earth system interactions for sustainable food production via expert elicitation

Several safe boundaries of critical Earth system processes have already been crossed due to human perturbations; not accounting for their interactions may further narrow the safe operating space for humanity. Using expert knowledge elicitation, we explored interactions among seven variables representing Earth system processes relevant to food production, identifying many interactions little explored in Earth system literature. We found that green water and land system change affect other Earth system processes strongly, while land, freshwater and ocean components of biosphere integrity are the most impacted by other Earth system processes, most notably blue water and biogeochemical flows. We also mapped a complex network of mechanisms mediating these interactions and created a future research prioritization scheme based on interaction strengths and existing knowledge gaps. Our study improves the understanding of Earth system interactions, with sustainability implications including improved Earth system modelling and more explicit biophysical limits for future food production.

Application of a Machine Learning Approach Based on Nearest Neighbors to Extract Embrittlement Trends from RPV Surveillance Data

Over the past 10-15 years considerable effort by many different researchers has produced codified embrittlement trend curves for use in calculations that support the safe life management of nuclear reactor pressure vessels. This paper explores the complementary insights made possible by a more localized approach to data fitting using nearest-neighbor techniques. Our objective is to evaluate the accuracy and precision of nearest neighbor predictions of transition temperature shift (ΔT41J) using a comprehensive database of international surveillance data. In the nearest neighbor method, a distance vector is used to quantify the proximity (and thereby the similarity) of all known conditions to some condition of interest. This paper evaluated the effect of different distance vector and partition criteria choices. Higher dimensional distances appear to offer the promise of greater embrittlement trend fitting accuracy. However, this accuracy reduces the ability to apply the method to all conditions encountered in the fleet. As our goal is to identify data from one plant that can be used to inform embrittlement trends in other plants (e.g., as is done in integrated surveillance programs), it seems appropriate to adopt the simplest distance vector that offers reasonable accuracy (i.e., copper, nickel, temperature). We combined this distance, which ranks the similarity of irradiation sensitivity between different conditions, with a copper measurement precision of ± 0.03 mass% that serves as a trigger to determine the (Cu, Ni, T) distance to the partition limit (called ρ). When used with the surveillance database, this approach indirectly limits the nickel and temperature variation within the partition, making explicit limits on nickel and temperature unnecessary. While some effect of copper on ΔT41J within the partition remains, it has little practical effect on the mean nearest neighbor trend curve while slightly widening the tolerance bounds, which can be viewed as a conservatism.

On the Incompressible Behavior in Weakly Nonlinear Elasticity

This article considers the influence of incompressibility on the compliance and stiffness constants that appear in the weakly nonlinear theory of elasticity. The formulation first considers the incompressibility constraint applied to compliances, which gives explicit finite limits for the second-, third-, and fourth-order compliance constants. The stiffness/compliance relationships for each order are derived and used to determine the incompressible behavior of the second-, third-, and fourth-order stiffness constants. Unlike the compressible case, the fourth-order compliances are not found to be dependent on the fourth-order stiffnesses.

Who Answers for the Government? Bureaucrats, Ministers, and Responsible Parties

AbstractA key feature of parliamentary democracy is government accountability vis‐à‐vis the legislature, but the important question of who speaks for the government—cabinet ministers or unelected bureaucrats, and the institutional underpinnings of this behavior—receives scant attention in the existing literature. We investigate this question using the case of Japan, and data on more than four million committee speeches spanning distinct electoral and legislative institutional environments. We document how a party‐strengthening electoral system reform in 1994 facilitated a dramatic shift in the nature of government accountability to parliamentary committees: speeches by ministers increased, speeches by bureaucrats decreased, and discursive accountability between ministers and opposition legislators increased. Subsequent legislative reforms expanding junior ministerial roles and placing explicit limits on bureaucratic participation further reinforced the effects. These findings shed new light on the institutional foundations of responsible party government in general as well as its progressive development in Japan.

P–351 Ethical challenges posed by an increase of surplus frozen embryos in Argentinean fertility centers

Abstract Study question Can an increase in the quantity of frozen embryos lead to more difficulties in embryo disposition decisions (EDD)? Summary answer EDD posed clinical and ethical challenges and might be influenced by having more available embryos, due to changes in the laboratory procedures. What is known already Previous research suggests that many people find EDD difficult and emotionally distressing. Patients face ambivalence during the decision-making process which could lead to embryo abandonment. Regulation of embryo dispositions varies among countries, but in the Latin American context, the regulatory gap generates insecurities in healthcare professionals. Cultural values towards the embryo can be associated with discomfort, guilt, or psychological burden. Studies suggest that patients often feel that they are unable to make a satisfactory decision when presented with the current embryo disposition options. Thus, other ‘solutions’, such as the request for nonreproductive transfer, appear and raises ethical questions and concerns. Study design, size, duration This is an observational study which follows a thematic literature review, that identifies the main reasons for difficulties with embryo disposition decisions, in different countries. It focuses on the regulatory background of the principal ART providers worldwide to discuss the best course of action for Argentina, that faces the problem of EDD at a regulatory level. To inform the discussion, a comparative survey from an Argentinean context, was carried out. Participants/materials, setting, methods Most fertility clinics in Argentina are private entities, as there are very few public providers. Access to ART treatments has been regulated since 2013, but the law fails to define a number of important issues, including EDD and national registries. An online survey was sent to all reproductive facilities to collect data on storage content and the results were complemented with data from the Latin American Register (RedLara) and the Argentine Registry of Assisted Fertilization. Main results and the role of chance The survey results showed that in 2017, there were approximately 54.432 frozen embryos stored in 46 Argentinean fertility centers and the total amount in 2020 reached 91.724 stored in 54 centers. Despite the number of treatment cycles (IVF + OD) being constant between 2017 and 2020 (with a slight increase of 8%), the number of frozen embryos has increased exponentially (by 68.5%). This is a consequence of the improvements in cryopreservation techniques (vitrification) and the development of more efficient ovarian stimulation protocols, that have facilitated a rise in elective single embryo transfer. These advances, coupled with an inefficient regulatory framework, generate uncertainties in physicians who might already be conflicted and therefore provide little or inadequate guidance for patients facing EDD. Three strategies could be implemented to facilitate EDD under this particular setting. First, counseling sessions at different treatment stages should be encouraged and are conducted by trained mental health professionals, who are aware of their patient’s changing attitudes towards surplus embryos. Second, both aneuploid embryos and embryos which were cryopreserved more than 10 years ago could form part of a national bank for research purposes, using classified storage content. Third, promote effective regulation that includes EDD and explicit storage limits. Limitations, reasons for caution The influence of the Catholic Church on policy makers regarding embryo dispositions is the main drawback. There is a need to foster a regulatory framework that considers the changes in IVF procedures and practices. On a practical level, psychosocial care is missing as part of healthcare teams’ practices. Wider implications of the findings: The survey results revealed that IVF centers in Argentina will face an increase in euploid, aneuploid and untested frozen embryos, due to the changes registered in laboratory procedures. This tendency shows the need to discuss EDD with patients from the beginning of fertility treatment, through to its conclusion. Trial registration number Not applicable

P-351 Ethical challenges posed by an increase of surplus frozen embryos in Argentinean fertility centers

Abstract Study question Can an increase in the quantity of frozen embryos lead to more difficulties in embryo disposition decisions (EDD)? Summary answer EDD posed clinical and ethical challenges and might be influenced by having more available embryos, due to changes in the laboratory procedures. What is known already Previous research suggests that many people find EDD difficult and emotionally distressing. Patients face ambivalence during the decision-making process which could lead to embryo abandonment. Regulation of embryo dispositions varies among countries, but in the Latin American context, the regulatory gap generates insecurities in healthcare professionals. Cultural values towards the embryo can be associated with discomfort, guilt, or psychological burden. Studies suggest that patients often feel that they are unable to make a satisfactory decision when presented with the current embryo disposition options. Thus, other ‘solutions’, such as the request for nonreproductive transfer, appear and raises ethical questions and concerns. Study design, size, duration This is an observational study which follows a thematic literature review, that identifies the main reasons for difficulties with embryo disposition decisions, in different countries. It focuses on the regulatory background of the principal ART providers worldwide to discuss the best course of action for Argentina, that faces the problem of EDD at a regulatory level. To inform the discussion, a comparative survey from an Argentinean context, was carried out. Participants/materials, setting, methods Most fertility clinics in Argentina are private entities, as there are very few public providers. Access to ART treatments has been regulated since 2013, but the law fails to define a number of important issues, including EDD and national registries. An online survey was sent to all reproductive facilities to collect data on storage content and the results were complemented with data from the Latin American Register (RedLara) and the Argentine Registry of Assisted Fertilization. Main results and the role of chance The survey results showed that in 2017, there were approximately 54.432 frozen embryos stored in 46 Argentinean fertility centers and the total amount in 2020 reached 91.724 stored in 54 centers. Despite the number of treatment cycles (IVF + OD) being constant between 2017 and 2020 (with a slight increase of 8%), the number of frozen embryos has increased exponentially (by 68.5%). This is a consequence of the improvements in cryopreservation techniques (vitrification) and the development of more efficient ovarian stimulation protocols, that have facilitated a rise in elective single embryo transfer. These advances, coupled with an inefficient regulatory framework, generate uncertainties in physicians who might already be conflicted and therefore provide little or inadequate guidance for patients facing EDD. Three strategies could be implemented to facilitate EDD under this particular setting. First, counseling sessions at different treatment stages should be encouraged and are conducted by trained mental health professionals, who are aware of their patient’s changing attitudes towards surplus embryos. Second, both aneuploid embryos and embryos which were cryopreserved more than 10 years ago could form part of a national bank for research purposes, using classified storage content. Third, promote effective regulation that includes EDD and explicit storage limits. Limitations, reasons for caution The influence of the Catholic Church on policy makers regarding embryo dispositions is the main drawback. There is a need to foster a regulatory framework that considers the changes in IVF procedures and practices. On a practical level, psychosocial care is missing as part of healthcare teams’ practices. Wider implications of the findings The survey results revealed that IVF centers in Argentina will face an increase in euploid, aneuploid and untested frozen embryos, due to the changes registered in laboratory procedures. This tendency shows the need to discuss EDD with patients from the beginning of fertility treatment, through to its conclusion. Trial registration number not applicable

Quantum machine learning with adaptive linear optics

We study supervised learning algorithms in which a quantum device is used to perform a computational subroutine – either for prediction via probability estimation, or to compute a kernel via estimation of quantum states overlap. We design implementations of these quantum subroutines using Boson Sampling architectures in linear optics, supplemented by adaptive measurements. We then challenge these quantum algorithms by deriving classical simulation algorithms for the tasks of output probability estimation and overlap estimation. We obtain different classical simulability regimes for these two computational tasks in terms of the number of adaptive measurements and input photons. In both cases, our results set explicit limits to the range of parameters for which a quantum advantage can be envisaged with adaptive linear optics compared to classical machine learning algorithms: we show that the number of input photons and the number of adaptive measurements cannot be simultaneously small compared to the number of modes. Interestingly, our analysis leaves open the possibility of a near-term quantum advantage with a single adaptive measurement.

Universal break law for a class of models of polymer rupture

We model a polymer by a finite chain of Brownian particles, interacting through a pairwise potential U. We investigate what happens when one end of the chain is fixed and the other end slowly pulled away, and when we assume that the chain breaks as soon as the distance between two neighbouring particles exceeds a certain threshold b. We find that under natural conditions on U and suitable scaling of noise and pulling speed, the laws of the break time and of the place along the chain where the break occurs converge to explicit limits. These limits are universal in the sense that they only depend on U″(b).

Universal break law for a class of models of polymer rupture

We model a polymer by a finite chain of Brownian particles, interacting through a pairwise potential U. We investigate what happens when one end of the chain is fixed and the other end slowly pulled away, and when we assume that the chain breaks as soon as the distance between two neighbouring particles exceeds a certain threshold b. We find that under natural conditions on U and suitable scaling of noise and pulling speed, the laws of the break time and of the place along the chain where the break occurs converge to explicit limits. These limits are universal in the sense that they only depend on U”(b).

Biological mechanisms may contribute to soil carbon saturation patterns.

Increasing soil organic carbon (SOC) storage is a key strategy to mitigate rising atmospheric CO2 , yet SOC pools often appear to saturate, or increase at a declining rate, as carbon (C) inputs increase. Soil C saturation is commonly hypothesized to result from the finite amount of reactive mineral surface area available for retaining SOC, and is accordingly represented in SOC models as a physicochemically determined SOC upper limit. However, mineral-associated SOC is largely microbially generated. In this perspective, we present the hypothesis that apparent SOC saturation patterns could emerge as a result of ecological constraints on microbial biomass-for example, via competition or predation-leading to reduced C flow through microbes and a reduced rate of mineral-associated SOC formation as soil C inputs increase. Microbially explicit SOC models offer an opportunity to explore this hypothesis, yet most of these models predict linear microbial biomass increases with C inputs and insensitivity of SOC to input rates. Synthesis of 54 C addition studies revealed constraints on microbial biomass as C inputs increase. Different hypotheses limiting microbial density were embedded in a three-pool SOC model without explicit limits on mineral surface area. As inputs increased, the model demonstrated either no change, linear, or apparently saturating increases in mineral-associated and particulate SOC pools. Taken together, our results suggest that microbial constraints are common and could lead to reduced mineral-associated SOC formation as input rates increase. We conclude that SOC responses to altered C inputs-or any environmental change-are influenced by the ecological factors that limit microbial populations, allowing for a wider range of potential SOC responses to stimuli. Understanding how biotic versus abiotic factors contribute to these patterns will better enable us to predict and manage soil C dynamics.

Some Reflections on the Constitutional Review in Albania in a Comparison Key

In this study we will try to analyze the foundations of the Constitution as a pillar and as a guarantee for its solidity. The study will also address the need for revision of the constitution as a fundamental element of its existence and continuity. Particular emphasis will be given to the comparison of the constitutions of the most important countries in the world as regards the procedures and limits to the constitutional revision. In this sense, the constitutions of some Balkan Peninsula countries will be analyzed to draw a comparison and analyze the Albanian Constitution as regards the procedure for its revision. The study intends to analyze the procedures for the revision of the Constitution as well as the explicit and implicit limits to these revisions. In the Constitutional revision in Albania in 2016, the role of the Constitutional Court on the control of the constitutional legitimacy of constitutional revision laws was clarified. Formal constitutionality is usually emphasized since the Albanian constitutional reform underlined that the Constitutional Court in Albania could express itself on the constitutionality of the Constitutional revision law only from a formal point of view.
 
 Received: 2 January 2021 / Accepted: 27 February 2021 / Published: 7 March 2021

Trade-offs in fishery management objectives when allowing catch limit carry-over between years

Abstract Fisheries managed with explicit annual catch limits often have realized catches below the total allowable catch. Carry-over provisions allowing aggregate or individual carry-forward of catch underages are included in many fishery management systems, but the ramifications of these provisions on different fishery management objectives such as average catch, variability in catch, and probability and degree of overfishing are not well understood. We developed a management strategy evaluation simulation to explore performance of alternative carry-over policies assuming different life histories and under different causes of catch underages. We evaluated the impacts of the carry-overs across common management objectives to understand the trade-offs associated with different amounts of allowable carry-over. We find that carry-overs can increase yield to the fishery but can also increase the risks of overfishing, low stock biomass, low catch, and the interannual variability in catch. All of these risk measures increase with the amount of carry-over allowed in most cases, but for cases of low stock productivity or positively biased stock assessment estimates, larger carry-over allowances resulted in similar or lower yield compared to smaller allowances. The analysis suggests that some benefits of carry-over can be maintained and risks can be limited by restricting the maximum carry-over allowed.

Operational limits for aquaculture operations from a risk and safety perspective

Current decision making regarding whether to abort a high-risk aquaculture operation in a Norwegian fish farm is mainly experience-driven. The on-site personnel decides whether to start/delay/abort operations primarily based on their subjective judgement about whether they can handle the situation. The risk is considered implicitly as “gut feelings”. There are no explicit operational limits nor a structured process to derive these for high-risk operations. In this research, a predefine safety-critical attributes have been identified from major accident scenarios to guide machine learning process to define operational limits based on multi-source data. Bayesian network, Tree Augmented Naïve Bayes (TAN) search algorithms were selected to build up prediction model so that operational limits upon a given condition can be decided. The paper concludes that machine learning techniques have great potential to be used to support safe decision-making in high-risk aquaculture operation, and the risk-based operational limits facilitates better understanding of operational context, and comprehension of the meaning of several deviations which may indicate a dangerous situation.

Provisioning systems for a good life within planetary boundaries

The concept of provisioning systems has recently emerged as a promising way to understand the differences between levels of resource use and social outcomes observed across societies. However, the characteristics of provisioning systems remain poorly understood. Here, we make a new contribution to conceptualising provisioning systems and to understanding differences in the resource efficiency with which they achieve social outcomes. We define a provisioning system as a set of related elements that work together in the transformation of resources to satisfy a foreseen human need. We analyse six theories in terms of their contribution to understanding provisioning systems within the biophysical and social constraints of Raworth’s “Safe and Just Space” framework. We find that most of these theories fail to prioritise human needs and well-being, and do not incorporate explicit environmental limits. However, they provide important insights that we draw upon to identify six important provisioning system elements (households, markets, the commons, the state, techniques, and material stocks). Based on the theories, we also identify two important relationships between elements, namely feedbacks and power relations. We further propose the concept of “appropriating systems” as a component of provisioning systems. Appropriating systems reduce the resource efficiency of human well-being via rent extraction, and act as a barrier to meeting human needs at a sustainable level of resource use. We combine these concepts into a new framework, and discuss applications to energy systems.

Parliamentary Prorogation in Comparative Context

AbstractThis paper examines the power to prorogue (or suspend) Parliament following the 2019 prorogation controversy in the UK. We outline the legal basis of prerogative‐based prorogation, survey its uses in the UK and other Westminster systems, and compare it with equivalent rules in other European parliamentary democracies. The comparative perspective highlights the outlier status of the UK among comparable European democracies. In the UK, the absence of explicit legal limits on the use of prorogation gives the executive exceptional scope to employ the power for political purposes to sidestep Parliament. We conclude by discussing the implications of these findings for current discussions about the desirability of reforming the UK’s prorogation rules and placing express legal limits on the executive’s power.

An amplitude- and rate-saturated collective pitch controller for wind turbine systems

This paper proposes a new collective pitch controller for wind turbine systems to maintain the generator speed constant at the rated value in the region above the rated wind speed. It provides the command of the collective pitch angle to the wind turbine system, and one can impose explicit limits on the magnitude and the rate-of-change of the pitch angle command. In addition, the controller involves a variable gain that realizes non-overshooting convergence from the large errors in the generator speed and accurate regulation of the generator speed near the rated value. This controller is an extension of an amplitude- and rate-saturated controller previously proposed by the authors. It is combined with a state and disturbance observer and a lookup table-based feedforward. The proposed controller is validated through a software simulator FAST emulating a three-bladed horizontal-axis wind turbine system.

Who Answers for the Government? Institutional Reform and Ministerial Accountability in Japan

A key feature of parliamentary democracy is government accountability vis-a-vis the legislature, but the important question of who speaks for the government—cabinet ministers or unelected bureaucrats, and the institutional underpinnings of this behavior—receives scant attention in the existing literature. We investigate this question with the case of Japan, and data on more than 4 million committee speeches spanning distinct electoral and legislative institutional environments. We document how a party-strengthening electoral system reform in 1994 facilitated a dramatic shift in the nature of government accountability to parliamentary committees: speeches by ministers increased, speeches by bureaucrats decreased, and discursive accountability between ministers and opposition legislators increased. Subsequent legislative reforms expanding junior ministerial roles and placing explicit limits on bureaucratic participation further reinforced the effects. These findings shed new light on the institutional foundations of responsible party government in general, as well as its progressive development in Japan.